1. Field of the Invention
This invention relates to a process for the reforming of naphtha intended for use as automobile fuel.
2. Discussion of the Prior Art
As is well known, automobile fuel or gasoline is derived from crude oil. The naphtha fraction boiling at about 175.degree. to 445.degree. C. obtained from crude oil by distillation is called straight-run or virgin naphtha. Such naphtha has a low octane rating, and its octane rating must be increased before it can be used as the gasoline of commerce.
According to conventional practice, the octane rating of straight-run naphtha is increased by catalytic reforming. In a typical reforming process, the naphtha heated to about 780.degree.-1000.degree. F. is contacted with a reforming catalyst, such as platinum on alumina. Since the reaction involved in reforming are endothermic, reforming is best effected in a series of reactors with the naphtha being pre-heated prior to passage to each reactor.
As is well known, a variety of reactions occur during reforming. The compounds contained in the naphtha, mainly hydrocarbons, are isomerized to more highly branched compounds or are converted to cyclic compounds. Cycloparaffins (naphthenes) are dehydrogenated to aromatic compounds, mainly benzene, toluene and xylene (BTX). The amount and distribution of the aromatic compounds produced varies considerably depending on the nature of the naphtha feedstock and the reforming conditions utilized. On average, catalytic reforming yields a reformate containing about 8% by weight of benzene, about 10% by weight of toluene, and about 15% by weight of xylene and ethylbenzene.
In recent years, benzene has been recognized as being a carcinogen, and the desirability of reducing exposure to benzene has become apparent. Accordingly, it is an object of the present invention to provide an improved reforming process which produces gasoline having an acceptable octane rating, but a lowered content of benzene.